The present invention generally relates to inkjet printing, and in particular to a specific ink set with high lightfastness dye for improving inkjet image quality.
The use of inkjet printing systems has grown dramatically in recent years. This growth may be attributed to substantial improvements in print resolution and overall print quality coupled with appreciable reduction in cost. Today""s inkjet printers offer acceptable print quality for many commercial, business, and household applications at costs fully an order of magnitude lower than comparable products available just a few years ago. Notwithstanding their recent success, intensive research and development efforts continue toward improving inkjet print quality. In general, inkjet print quality still falls short of that produced by more expensive technologies such as photography and offset or gravure printing. A surge in interest in inkjet imaging (e.g., the rendition of pictures) has resulted in the need to produce near photographic quality printed images at a reasonable cost. The challenge remains to further improve the image quality and lightfastness of inkjet printed images, especially images containing skin tones, without increasing their cost.
Color inkjet printers typically use three inks of differing hues: magenta, yellow, and cyan, and optionally black. The particular set of colorants, e.g., dyes, used to make the inks is called a xe2x80x9cprimary dye set.xe2x80x9d A spectrum of colors, e.g., secondary colors, can be generated using different combinations of the primary dye set. In printing processes such as lithography, dye transfer, and some types of thermal transfer, it is possible to vary spot size so that less is demanded of the primary colored inks when producing a good secondary. When the colored inks are used in a binary printing device, that is, one in which a dot of color is either present or absent, e.g., a thermal inkjet printer, the ability of the primaries to give recognizable secondaries is even more important.
If such an ink is to be used in an inkjet printing device, characteristics such as crusting, long-term stability, and materials compatibility must also be addressed. If the ink is to be used in a thermal inkjet printer, the further constraint of being thermally stable (kogation-resistant) is added.
In general, a successful ink set for color inkjet printing must be compatible with the inkjet pen and printing system. Some of the required properties for the inkjet ink include: good crusting resistance, good stability, the proper viscosity, the proper surface tension, little color-to-color bleed, rapid dry time, no negative reaction with the vehicle, high solubility of the dyes in the vehicle, consumer safety, low strike through, high color saturation, and good dot gain.
Furthermore, the colored characteristics of the colorants play an important role in the quality of the printed inkjet image. Color inkjet inks have been designed and tailored for printing business graphics such as depiction of information in the form of xe2x80x9cpie-chartsxe2x80x9d and xe2x80x9cbar-chartsxe2x80x9d on plain paper. These applications require that inkjet use bright, vivid, high chroma colorants that, in general, are not lightfast. Generally, these dyes, although suitable for business graphics, do not provide a xe2x80x9ctruexe2x80x9d photographic lightfastness especially in the lower portion of the tone scales. Chroma describes how much color or how vivid an object is. In the CIE L*a*b* system, the lightness or L* is a good measure of chroma with a low L* value being very dark.
One attribute that is particularly important in imaging (i.e., color rendition of pictures) is xe2x80x9cgrainxe2x80x9d. Grain describes how visible the dots are to the viewer. If large, dark drops are used, the dots become very visible and image quality is degraded. One technique to reduce grain is to use smaller drop weight to produce nearly invisible drops. The downsides to this technique are more difficult and more costly manufacturing processes due to the requirement for smaller orifice holes and resistors and more difficult reliability challenges due to the smaller holes. Another technique is to use additional xe2x80x9clightxe2x80x9d inks such as a light magenta or cyan at colorant loadings 5-25% of the normal or dark ink. This technique allows the use of larger, low colorant load drops. These xe2x80x9clightxe2x80x9d drops are less visible due to the presence of less colorant. One downside to this approach is that these xe2x80x9clightxe2x80x9d inks fade much faster on media than the dark inks. This fade often occurs in critical areas such as the skin tone of a human being. Thus, there is a need for more lightfast colorants to be used in these light inks.
Investigations continue into developing ink formulations which have improved properties and which do not improve one property at the expense of the others. Thus, the challenge remains to further improve the image quality and lightfastness of the inkjet prints without sacrificing pen performance and reliability.
In one embodiment, the present invention relates to a set of inkjet inks for inkjet printing, comprising: a light magenta ink comprising a high lightfastness magenta dye.
In another embodiment, the present invention relates to a set of inkjet inks for inkjet printing, comprising: a light cyan ink comprising a high lightfastness cyan dye.
In yet another embodiment, the present invention relates to a set of inkjet inks for inkjet printing, comprising: a light yellow ink comprising a high lightfastness yellow dye.
In still another embodiment, the present invention relates to a set of inkjet inks for inkjet printing, comprising: a light black ink comprising a high lightfastness black dye.
In another embodiment, the present invention relates to a method for inkjet printing, the method comprising the step of ejecting ink from an inkjet, the ink comprising a light magenta ink, the light magenta ink comprising a high lightfastness magenta dye.
In yet another embodiment, the present invention relates to a method for inkjet printing, the method comprising the step of ejecting ink from an inkjet, the ink comprising a light cyan ink, the light cyan ink comprising a high lightfastness cyan dye.
In still another embodiment, the present invention relates to a method for inkjet printing, the method comprising the step of ejecting ink from an inkjet, the ink comprising a light yellow ink, the light yellow ink comprising a high lightfastness yellow dye.
In another embodiment, the present invention relates to a method for inkjet printing, the method comprising the step of ejecting ink from an inkjet, the ink comprising a light black ink, the light black ink comprising a high lightfastness black dye.